An operating system (commonly abbreviated as either OS or O/S) is an interface between hardware, software and user. Examples would be Windows Vista, Windows 7, Mac OS or Linux. The OS provides hardware management and controls multitasking. Without an OS, a computer can not work to its full potential and most programs require an OS to function.
Chomium - Google's new computer OS:
3.3.2 Roles of the Operating Systems
Communicating with peripherals
Coordinating concurrent processing of jobs
Memory management
Resource monitoring
Accounting and security
Program and data management
Providing appropriate user interfaces
3.3.3 Computer Systems
Multi-user is a term that defines an operating system or application software that allows concurrent access by multiple users of a computer. Time-sharing systems are multi-user systems.
Single-user, the complementary term, is most commonly used when talking about an operating system being usable only by one person at a time such as for a client which connects to a server.
Multitasking is a method by which multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is actively executing instructions for that task. Multitasking solves the problem by scheduling which task may be the one running at any given time, and when another waiting task gets a turn. The act of reassigning a CPU from one task to another one is called a context switch. When context switches occur frequently enough the illusion of parallelism is achieved. Even on computers with more than one CPU (called multiprocessor machines), multitasking allows many more tasks to be run than there are CPUs.
Single tasking is when computers are only able to run one task at a time.
Advantages and Disadvantages of Multitasking
To the user, the advantage of multitasking is the ability to have several applications open and working at the same time. For example, a user can edit a file with one application while another application is recalculating a spreadsheet.
To the application developer, the advantage of multitasking is the ability to create applications that use more than one process and to create processes that use more than one thread of execution. For example, a process can have a user interface thread that manages interactions with the user (keyboard and mouse input), and worker threads that perform other tasks while the user interface thread waits for user input. If you give the user interface thread a higher priority, the application will be more responsive to the user, while the worker threads use the processor efficiently during the times when there is no user input.
The data is collected before any processing takes place; it is then entered into the system in one go (a batch of data) and processed.
Online/interactive
The data is entered and processed right away.
Real-time
This is a subset of online processing - the data is entered and processed right away. This is done quickly, the processing of data must be completed and produce an output in time to affect the next input.
3.3.6 Applicatins of different processing
Different processes are used in different situations. For example, batch processing systems are used in payroll cheque processing. As mentioned above, the key characteristic of batch processing is that all the data is collected first. In the simplest of payroll systems the hours worked by each employee need to be collected; similarly in cheque-processing systems a batch of cheques are collected to be input into the system in one go.
A systems flow chart is often used to describe such processes:
In cheque processing the cheque data is not input by hand but a direct data entry method is used. This will either be Optical Character Recognition (OCR) or Magnetic Ink Character Recognition (MICR ).
In this case the amount of money on the cheque will be encoded and then the appropriate amount can be deducted from the payer's account and added to the payee's account. Again, this is a simple view of the process. Interactive (online) processing (including word processing & computer games):
In normal usage on-line means that a device is under the control of a computer but online has come to mean connected to a network or other computer system (in particular online relates to internet usage by people). The two terms are commonly used interchangeably.
Interactive or online processing means that data is processed by the system as it is entered - the user typically waits a short time for a response . Examples include booking systems (theatres, buses, airlines, hotels, etc) as well as applications like word-processing and games.
Because these applications respond right away to data input, the data files themselves are held on a fast-access medium such as a disc-drive. In addition, direct access would typically be used.
Real-time processing (including air traffic control and patient monitoring):
Real-time processing is fast; however, speed alone is not the only requirement. Some online systems, like the stock control system at a supermarket appear to operate instantaneously in reading barcodes and looking up prices.
The processing of input data and production of the output must take place in time to affect the next input to the system. For example, in the case of patient monitoring, a drug might be used to control the heartrate. The flow of this drug could be regulated by a computer system. Should the heartrate fall or stop, the drug flow must be altered immediately, before further readings are taken. In an air traffic control monitoring system, the display must be updated immediately the direction, speed, or height of the plane is altered.
Real-time processing is often associated with automatic data entry , this is when data is read from a sensor or other input device without human interaction.
3.3.7 - Master and Transaction Files
A Master file contains the main data for a computer system or application. A transaction file typically hold a list of the changes that need to be made to the data held in the master file. A change is referred to as a transaction. The transaction file is a temporary file used to update the master file.
In order to efficiently update to create a new master file, the master and transaction files need to be sorted. This may allow the process to take place in one pass.
3.3.8 - Reliability
The reliability of Computer Systems varies according to the nature of the task they carry out. In some cases it is not a complete disaster if they fail - eg if the hard disc on your computer crashes and destroys your homework it may or may not be a terrible event.
Computer systems dealing with commerce can be vital to personal and national economies ; large banks, insurance companies, airlines and shipping lines for example. In these types of system, data is backed up both on site and off site. Terrible as the bombing of New York's twin towers was, businesses based there were able to carry on thanks to the fact that the data was safely backed up elsewhere.
Yet other computer systems maintain safe operations, eg air traffic control, hospital patient monitoring systems, nuclear power station control systems, etc. In these cases, mirrored systems are often used so that if one fails, the other is immediately ready to take over. In extreme cases, triple systems may be used.
We noted already on the previous sub-section that a master file can be re-created from the previous master file and the transaction file. In batch processing , three generations of master and transaction files are usually kept. This is sometimes called the Grandfather, Father, Son method of backup.
Backup utilities are also used to keep copies of important files. These backups maybe full (a new copy made of every file on the system) or incremental (only new and changed files are saved) Best content in StJulians_ComputerScience | Diigo - Groups
3.3.1 Operating Systems
An operating system (commonly abbreviated as either OS or O/S) is an interface between hardware, software and user. Examples would be Windows Vista, Windows 7, Mac OS or Linux. The OS provides hardware management and controls multitasking. Without an OS, a computer can not work to its full potential and most programs require an OS to function.
Chomium - Google's new computer OS:
3.3.2 Roles of the Operating Systems
3.3.3 Computer Systems
Advantages and Disadvantages of Multitasking
To the user, the advantage of multitasking is the ability to have several applications open and working at the same time. For example, a user can edit a file with one application while another application is recalculating a spreadsheet.
To the application developer, the advantage of multitasking is the ability to create applications that use more than one process and to create processes that use more than one thread of execution. For example, a process can have a user interface thread that manages interactions with the user (keyboard and mouse input), and worker threads that perform other tasks while the user interface thread waits for user input. If you give the user interface thread a higher priority, the application will be more responsive to the user, while the worker threads use the processor efficiently during the times when there is no user input.
3.3.4 Types of Computers
3.3.5 Types of processing
3.3.6 Applicatins of different processing
Different processes are used in different situations. For example, batch processing systems are used in payroll cheque processing. As mentioned above, the key characteristic of batch processing is that all the data is collected first. In the simplest of payroll systems the hours worked by each employee need to be collected; similarly in cheque-processing systems a batch of cheques are collected to be input into the system in one go.
A systems flow chart is often used to describe such processes:
In cheque processing the cheque data is not input by hand but a direct data entry method is used. This will either be Optical Character Recognition (OCR) or Magnetic Ink Character Recognition (MICR ).
In this case the amount of money on the cheque will be encoded and then the appropriate amount can be deducted from the payer's account and added to the payee's account. Again, this is a simple view of the process.
Interactive (online) processing (including word processing & computer games):
In normal usage on-line means that a device is under the control of a computer but online has come to mean connected to a network or other computer system (in particular online relates to internet usage by people). The two terms are commonly used interchangeably.
Interactive or online processing means that data is processed by the system as it is entered - the user typically waits a short time for a response . Examples include booking systems (theatres, buses, airlines, hotels, etc) as well as applications like word-processing and games.
Because these applications respond right away to data input, the data files themselves are held on a fast-access medium such as a disc-drive. In addition, direct access would typically be used.
Real-time processing (including air traffic control and patient monitoring):
Real-time processing is fast; however, speed alone is not the only requirement. Some online systems, like the stock control system at a supermarket appear to operate instantaneously in reading barcodes and looking up prices.
The processing of input data and production of the output must take place in time to affect the next input to the system. For example, in the case of patient monitoring, a drug might be used to control the heartrate. The flow of this drug could be regulated by a computer system. Should the heartrate fall or stop, the drug flow must be altered immediately, before further readings are taken. In an air traffic control monitoring system, the display must be updated immediately the direction, speed, or height of the plane is altered.
Real-time processing is often associated with automatic data entry , this is when data is read from a sensor or other input device without human interaction.
3.3.7 - Master and Transaction Files
A Master file contains the main data for a computer system or application. A transaction file typically hold a list of the changes that need to be made to the data held in the master file. A change is referred to as a transaction. The transaction file is a temporary file used to update the master file.
In order to efficiently update to create a new master file, the master and transaction files need to be sorted. This may allow the process to take place in one pass.
3.3.8 - Reliability
The reliability of Computer Systems varies according to the nature of the task they carry out. In some cases it is not a complete disaster if they fail - eg if the hard disc on your computer crashes and destroys your homework it may or may not be a terrible event.
Computer systems dealing with commerce can be vital to personal and national economies ; large banks, insurance companies, airlines and shipping lines for example. In these types of system, data is backed up both on site and off site. Terrible as the bombing of New York's twin towers was, businesses based there were able to carry on thanks to the fact that the data was safely backed up elsewhere.
Yet other computer systems maintain safe operations, eg air traffic control, hospital patient monitoring systems, nuclear power station control systems, etc. In these cases, mirrored systems are often used so that if one fails, the other is immediately ready to take over. In extreme cases, triple systems may be used.
We noted already on the previous sub-section that a master file can be re-created from the previous master file and the transaction file. In batch processing , three generations of master and transaction files are usually kept. This is sometimes called the Grandfather, Father, Son method of backup.
Backup utilities are also used to keep copies of important files. These backups maybe full (a new copy made of every file on the system) or incremental (only new and changed files are saved)
Best content in StJulians_ComputerScience | Diigo - Groups